Linear copolymers of carbon monoxide and one or more ethylenically unsaturated compounds may be prepared by reacting the monomers under polymerization conditions with a catalyst system which comprises a Group VIII metal and a weakly or non-coordinating anion. The preparation of these copolymers may be carried out in the liquid phase. That is, the reaction can be conducted so that the continuous phase is formed by a liquid diluent such as a non-polymerizable liquid in which the catalyst dissolves but in which the formed copolymers are substantially insoluble. The recovery and purification of the product of such a process normally requires a filtration or centrifugation step. Moreover, a distillation step is usually required in order to recover pure diluent.
The preparation of the copolymers may also proceed in the gas phase. When this approach is taken the continuous phase is formed by gaseous carbon monoxide and possibly one or more of the other monomers if they are present in the gas phase under the prevailing polymerization conditions. The gas phase preparation of the copolymers is considered advantageous because product recovery is simpler than in the liquid phase process. The separation and purification steps inherent in the liquid phase process can also be omitted in gas phase production. This improves the economics of the process.
Considerable efforts have been made to increase the activity of the catalyst system. Some improvement has resulted from, for example, changing the reaction conditions or modifying the components participating in the catalyst. EP-A-239145 proposes an enhancement of catalytic activity by incorporating an oxidant such as a quinone in the catalyst system. Between about 1 and 10000 mol of quinone per gram atom of palladium are purportedly preferred with between about 10 and 100 mol per gram atom of palladium being set forth in the examples.
EP-A-272728 proposes that other oxidants are also suitable for enhancing the catalyst activity such as organic nitrites and nitro compounds. Quantities similar to those of the quinones are recited for the use such other oxidants. That is, large amounts of the oxidants are required.
Significant improvements in catalyst activity continue to be sought. Moreover, the art could benefit from such improvements particularly where the process occurs in the gas phase without large quantities of catalyst modifiers. Economically advantageous catalyst systems such as those which do not require separate or discrete additions of catalyst promoter are also needed.